Method and apparatus for producing calendered paper or board

ABSTRACT

A method and an arrangement for manufacturing calendered paper or board particularly in the on-line manufacturing method. In the method, a base web is formed from a mixture of water and pulp supplied from the headbox and the web is dried by removing water over the press section and over the dryer section by heating. The formed web is calendered at least once to modify the surface on at least one of its sides. Before calendering the cross-direction thickness profile of the web is standardized and calendering is carried out by means of a long-nip calender, whereby good surface quality is obtained without losing the bulk or stiffness of the web.

FIELD OF THE INVENTION

The present invention relates to a method for producing paper or boardin a system where the manufactured base web is treated by means of atleast one calendar for improving its surface properties.

More specifically, a preferred embodiment of the invention relates toon-line calendering in which at least one calendering step is carriedout immediately after the manufacture of the base web without anyintermediate reeling.

The invention also relates to an arrangement for implementing themethod.

BACKGROUND OF THE INVENTION

The invention particularly concerns the manufacture of paper or board byusing on-line calendering. In on-line calendering, the calender isarranged immediately after the paper or board machine or a coating lineand the web is taken directly to the calender without any intermediatereeling. Conventionally, machine calenders where the web travels betweentwo hard rolls have been used as on-line calenders. Today, softcalendersare becoming more and more common because of the better surface glossthey achieve. Striving for improved surface gloss and smoothness hasfurther prompted the development of multi-nip calenders suited foron-line calendering. The maximum production speed of the supercalendersused previously has been insufficient, preventing their use inconnection with fast production lines.

The purpose of calendering is to increase smoothness and gloss and toimprove other properties of the printing surface of paper or board. Theimproved properties upgrade the quality of the final printed surface.The quality and printability of the printed surface a re among the mostimportant quality factors appreciated by paper users. Similarly, theprintability of printing board and the quality of the printed surfacethereof are important and, in addition, high stiffness and good bulk areoften appreciated. Furthermore, a factor affecting product quality isthe evenness of the c ross direction profile of the web, i.e., anyvariations in web thickness should be as small as possible in thecross-machine direction.

Surface smoothness of the product is achieved by exposing the fibrestructure of the product to high pressure and temperature by heating thehard calender rolls and by pressing the rolls against one another suchthat a high nip pressure is obtained in the nip between the rolls. Dueto these forces the fibres forming the web reach their glass transitiontemperature, and the deformation caused by the nip load is permanent.The gliding of the web surface against the roll surfaces may also giverise to alterations in fibre shape, thus enhancing the smoothing effect.

When multi-nip calendering has been used, the paper has usually beenmanufactured on a paper machine and thereafter coated, if desired. Inboth cases the coated or uncoated paper has been reeled onto storagerolls and calendered by means of separate calenders. The paper has beendried to a very low moisture content, typically about 1 to 3% of itstotal weight. Prior to calendering the paper is sufficiently wetted inorder to obtain good calendering results. A suitable moisture contentfor multi-nip calendering is approximately 6 to 10%. The purpose ofdrying to a low moisture content is to achieve an even cross directionmoisture content profile. The short storage time prior to thecalendering step also evens out the moisture content profile. In presenton-line calendering processes the web is dried to a high degree ofdryness whereafter it is rewetted before calendering, and thus, theprocess is similar to off-line calendering.

The web can be wetted e.g. by means of the water jet damping devicedescribed in U.S. Pat. No. 5,286,348, which achieves an even moisturecontent profile in the cross-machine direction of the web.

The above-described method which comprises first drying and thenrewetting the web is hampered by the time required by the absorption andevening out of the moisture, particularly in the thickness direction ofthe web and at the surface. If the wetting is performed immediatelybefore calendering, the uneven moisture content profile will affect thefinal surface properties and the quality grade of the paper may beimpaired.

Drying and rewetting increase the energy consumption during themanufacture of the product as well as the space required by theequipment when compared to a process which does dot require overdryingand rewetting prior to the calendering step. An uneven moisture content,e.g. surface moisture or an uneven moisture profile in some webdirection leads to changes in the properties of the web, such as glossor thickness profile because moisture has a strong impact on theworkability of the fibres. In the case of an uneven thickness profile,problems will occur in winding, which may even cause cross-directionwrinkles in customer rolls because even tightness is not achieved. Thewrinkles will reduce the runnability of the product in furtherprocessing e.g. during printing in other further processing machines,thus impairing the quality of the product from the customer's point ofview.

Moisture profile affects many factors in the manufacture of paper orboard as well as in the final quality of the product. One factor worthnoticing is that if fluctuations occur in moisture content, drier partsof the web will start to shrink before the wetter parts, which in turnwill lead to stretching of the wetter parts. Uneven stretching will thenlead to uneven drying shrink, which in turn leads to thicknessvariations and variations also in other properties of the product.

In modern machines, the moisture content of the paper or board web to bemanufactured is controlled in many ways particularly at the beginning ofweb formation. The most important target of controlling moisture contentprofile is good runnability of the machine and the product beingmanufactured, i.e. maximal production output within a given duration isstriven for. This is understandable because moisture content profile andtension profile are highly interdependent. Thus, the best possiblemoisture content profile has been striven for in such parts of themachine where the effect of dampness profile control on runnability isat its greatest. The dampness profile of the finished base web is thennot necessarily homogeneous and it is subject to tension. If the web isstored prior to calendering, the dampness will be evened out and thetensions will be relaxed, and thus, the evenness of the final dampnessof the web is of less importance. If, however, on-line calendering isused, the homogeneity of the final dampness has a strong effect onproduct quality and if the web moisture content is controlled by presentmethods and principles, the properties of calendered paper or board mayeven suffer, and the desired improvement in the properties of the finalproduct is not achieved. In multi-nip calenders, it is possible toexercise a relatively strong influence on the thickness profile of theweb, but in these calenders a very high nip pressure is applied,wherefore the calendering will usually lead to a significant reductionin thickness and bulk when compared to other calender types. Thus,multi-nip calendering is normally used in the manufacture of products ofwhich a high degree of smoothness and particularly gloss is expected.

One very important feature in the calendering process is thatcalendering is applied to obtain a slick and smooth surface withoutlosing any more stiffness or bulk than is necessary. As the surface ofpaper or board is subjected to even very high pressure duringcalendering depending on calender type, the web is compressed, wherebyits thickness is reduced and the web is compacted, in other words itsmass per volume is increased, i.e. its bulk is reduced. A reducedthickness and bulk of the web will naturally also result in reducedstiffness. As maximal stiffness and light weight per volume unit isnormally required of the product being manufactured, it is difficult tomatch the different effects of calendering with the properties of theend product.

On the other hand, calendering is used to standardize the thicknessprofile of the paper, i.e. to remedy thickness defects which may haveoccurred during web formation. The harder the surface of the rolls used,the easier it is to amend the profile, and thus a machine calender willusually obtain the best profile amendment results, and consequently,this is the most important field of use for this type of calenders.Today, a machine calender is used in many paper machines to finish thethickness profile and surface quality of paper such that they meet therequirements set for the final product. This has been so because thereare only limited ways of controlling the cross-direction thicknessprofile on a paper or board machine, and an acceptable thickness profilecannot be achieved without machine calendering. By means of machinecalendering it is possible to raise the surface quality of the productsuch that it meets end users' demands, but the properties of machinecalenders are limited when it comes to improving surface quality,wherefore no remarkable improvement in smoothness or gloss can beobtained by means of a machine calender. As the quality requirements setfor printing surfaces are constantly on the increase, other calenderingmethods must more and more often be used in addition to or instead ofmachine calendering.

Other types of calenders, such as soft-, long-nip or multi-nipcalenders, will obtain a considerably improved surface quality, but theyhave a much weaker thickness profiling capability than machinecalenders, mainly due to the softness of the surfaces on the parts whichpress the web. It is known that with a reduced tensile stiffness of thecalender roll coating, the thickness profiling capability of thecalender is impaired but its ability to produce a product with goodprinting properties is improved. As a machine calender has rolls of castiron or steel, they may have very hard surfaces, resulting in goodthickness standardization. On the other hand, the hard surface willexert stronger pressure on the web at its thicker and denser (harder)parts, wherefore the smoothing effect exerted on the web concerns thethicker parts of the web, and thus, surface properties will vary indifferent parts of the web.

SUMMARY OF THE INVENTION

The present invention aims at providing a method for manufacturingcalendered paper or board, enabling the manufacture of a product havinga uniform thickness profile, whereby the bulk of the web is reduced aslittle as possible, yet achieving good quality of the printing surface.

The invention is based on standardizing the cross-direction thicknessprofile of the base web prior to final calendering and performing thefinal calendering on a long-nip calender, for example a shoe calender.

In more detail, the method for producing a calendered product accordingto the present invention is characterized by standardizing thecross-directional thickness of the base web across a width of the baseweb to form a standardized web after forming the base web from a mixtureof water and pulp supplied from a headbox and and calendering diestandardized web at least once using a long-nip calender for modifyingat least one side of the standardized web.

The arrangement according to the invention, then, is characterized bymeans for standardizing a cross-direction thickness of the base webacross a width of the base web to form a standardized web after the baseweb is formed from a mixture of water and pulp fed from a headbox and along-nip calender for modifying at least one side of the standardizedweb arranged downstream of the means for standardizing.

The invention allows considerable savings in the pulp of the base web,because the bulk of the web is better by as much as 5 to 10% aftercalendering than that of a product manufactured using conventionalcalendering methods. This is of considerable advantage for the paper orboard manufacturer because the grammage of the product can be reducedwithout compromising its thickness and particularly its stiffness. Thus,it is possible for the manufacturer to have a smaller grammage and pulpconsumption and to still produce paper or board having unalteredstiffness. The surface and printability properties of the product aregood, as is its thickness profile. The good thickness profile results ingood customer rolls of even tightness in the longitudinal direction ofthe roll, whereby wrinkle formation is reduced. Rolls of uniformtightness and precisely cylindrical shape are easy to handle at theplant and particularly during further processing, and the rolls havegood runnability properties in further processing machines such asprinting machines.

The product surface has homogeneous properties over the entire surface,and alterations in surface quality occurring due to machine calenderingare avoided. The method according to the invention is well suited forraising the product quality of paper and board machines already inproduction e.g. in connection with modernizations. The invention isapplicable to off-line calendering but is of particular advantage inon-line systems where the optimization of the manufacture of the baseweb is more easily combined with the optimization of the calenderingevent.

The present solution is applicable to the manufacture of both uncoatedand coated products. In the manufacture of coated paper or board gradesthe coating step is carried out prior to the final calendering step,whereby a long-nip calender will obtain a very even and smooth surfaceand any unevenness of the base web will not show during visualinspection of the web, because the soft belt of a long-nip calender doesnot highlight unevenness as does e.g. the slightly harder roll coatingof a softcalender.

In the following, the invention is examined in more detail with the helpof a number of working examples and alternative embodiments.

Other objects and features of the invention will become apparent fromthe following detailed description.

In the following, the term long-nip calender is used to refer to acalender having a nip length of over 30 mm, typically 50 to 280 mm.

The purpose of calendering is to produce a good surface for paper orboard of which a good printing surface is required. It is of importancein the manufacture of both paper and especially board that the stiffnessof the product is reduced as little as possible. Often sufficientstiffness is of importance for the handling of the paper and in the caseof printable packing boards, among others, the material must be ofsufficient stiffness to enable the manufacture of strong packages.Previously known calendering methods provide reduced thickness andstiffness of the product, but the most modern long-nip calenders obtaingood surface quality with only small losses in stiffness or bulk. In thecase of a long-nip calender, a good surface is provided by means of asoft calendering surface, a relatively low surface pressure and a highthermoroll temperature. In a long-nip calender the calendering surfaceusually comprises a belt which is used to press the web against a heatedthermoroll. A roll can be used for pressing the belt, whereby the lengthof the nip is limited, or a shoe can be used whereby considerablepressing distances are achieved. Another advantage of the shoe calenderis that the length of the nip is adjustable as well as thecross-direction nip pressure distribution. The adjustment possibilitiesavailable are naturally dependent on the structure of the calender.

Another important purpose of a calendar is to amend the thicknessprofile of the product. As stated above, the thickness profile is bettereffected by a harder calendering surface. Thus, a long-nip calenderallows much less acting on the thickness profile than other calendersbecause the hardness of the calendering belt or other means used is lowwhen compared to the hardness of the rolls and roll coatings of othercalender types. Thus, a long-nip calender does not allow any significantinfluence to be exerted on the thickness profile even when azone-adjusted shoe calender is used.

On a paper or board machine the web is formed by feeding water and pulpfrom a headbox onto a wire or between two wires. The web having a highmoisture content is dried by removing water by pressing the web over thepress section and by heating it over the drying section by means of adrying cylinder, among others.

Today a number of devices are known which can be used to affect thethickness profile of the base web already during the formation step ofthe web, and consequently, web thickness can be standardized even beforeit enters the calender. Thus a long-nip calender may be used if thethickness profile of the web is standardized prior to calendering. Thethickness profile of the base web can be affected in many ways duringthe formation and drying of the entire web. The first possibility toaffect the web profile is in the headbox where the web is formed. In theheadbox the fibre content of the pulp to be fed onto a former wire orinto a twin wire can be adjusted e.g. by means of dilution adjustment byadding water into the pulp or, on the other hand, in the cross directionmore pulp may be fed to certain parts of the wire where needed. In thepress section of the machine, profiling steaming or compression may beapplied, and in the drying section, profiling drying or wetting.Actuators affecting the profile include e.g. a dilution-adjustedheadbox, a zone-adjusted press roll arranged in the press section or abelt-supported zone-adjusted press roll, a profiling steam box or wetteror a profiling web heater or cooler, e.g. a roll that is cooled zone byzone. Where a film transfer coater can be arranged prior to thecalender, the profiling can be carried out by using the coater to applywater or an adhesive mixture onto the web surface. Instead of a filmtransfer coater, e.g. a spray coater can be used which has a simpleconstruction and can be fitted even into a small space. The thicknessprofile of a web that has been dried to almost its final dryness can befurther adjusted by profiling wetting or a hard calender nip. If e.g. amachine calender is used for standardizing the thickness profile of theweb, it is of importance in the solution according to the invention thatthe nip load be kept small so as not to lose web thickness, bulk orstiffness during calendering. What is essential in the preferredembodiment of the invention is the optimization of the thickness profileadjustment of a paper or board machine for calendering.

The effect of the moisture content profile of the web and differences inmoisture content has been discussed in the Applicants' parallel PCTApplication No. FI98/00895, wherefore it may suffice in the presentcontext to say that altering the moisture content profile of the web canbe used to essentially affect the thickness profile. Said application isenclosed herein as reference.

According to the invention the thickness profile of the base web isstandardized prior to calendering and the calendering step is carriedout on a long-nip calender, preferably e.g. a shoe calender. As a shoecalender can no longer be used to essentially affect the thicknessprofile of the base web, the web must be of sufficiently homogeneousthickness already before calendering. The thickness profile can bestandardized using the above-mentioned equipment. In order to be able toimplement the method it must be ensured that the thickness of the baseweb has been standardized before the web enters the calender. For thisreason, profile measurement is needed before the calender. Profilemeasurement can be carried out at any stage before calendering but asthe thickness profile may be altered over the press section or duringdrying, there is cause to perform at least one measurement as close tothe calender as possible, preferably immediately before calendering.Thickness profile measurement can be carried out prior to the lastactuator which can be used to affect the thickness profile, whereby itis still possible to fix any possible profile defects by means of saidactuator. The minimum requirement is that the profile be measured atleast at one point prior to calendering and advantageously at least atone point prior to the last profiling instrument and immediately beforethe calender to ensure the fixing of any profile defect. After thecalender a final quality assurance measurement can be carried out.

One advantageous way of standardizing the web thickness profile is touse a machine calender equipped with hard rolls which is run at a lownip pressure. In this case the nip pressure of the machine calender mustbe kept extremely low and the aim is not to use it to affect themicroroughness of the surface. A machine calender can, however, be usedto even at low nip pressures effectively even out the thickness profile,simultaneously smoothing out the macroroughness of the surface, i.e.variations in the shape of the surface that are clearly greater than thefibre thickness. The method is particularly well suited for themanufacture of coated grades of board or paper, whereby machinecalendering is carried out prior to the first coating step and long-nipcalendering after coating. In the following an example of such a methodis described. The method is particularly well suited for the manufactureof liquid packaging board.

Conventionally, liquid packaging boards are coated twice becauseunbleached pulp is used for the core and bottom layers thereof, wherebya large amount of coating mix is required to obtain a surface ofsufficient brightness. As coating method, blade coating is most commonlyused, but even air brush coating is used because of its good opacity.Blade coating provides poor opacity and the air brush has poorrunnability and limited speed. In addition, background wetting isrequired in order to control warp.

According to the invention the board is first calendered by means of amachine calender or a softcalender using low nip pressure which isusually below 50 MPa, the nip length being less than 50, typically 1 to30 mm, and the surface temperature of the thermoroll being 80 to 300° C.When a softcalender is used, the coating has a hardness of 80 to 95 ShA.The purpose of precalendering is to alter the thickness profile andsurface roughness of the board such that they are at the level requiredby the following treatment steps without significantly reducing the bulkand stiffness of the board. Due to this requirement the board is notcalendered to have a fully smooth surface topography, instead, itsBendtsen roughness number may remain at a level below 700, typically 500to 600 ml/min. The precalendering step can be enhanced by steaming orwetting with water.

After precalendering precoating is carried out preferably by means of afilm transfer coater, whereby an opaque coat which well follows thesurface contour is obtained. A film transfer coater can be used tosimultaneously perform background wetting with water or a starchsolution, wherefore separate background wetting is not required. Thesusceptibility to breaks of a film transfer coater is also considerablylower than that of blade coaters. The front coat is provided at a rod orblade coating head where jet application is used for applying thecoating mix. The pressure impulse of a jet applicator is small whereforethe coat does not penetrate into the web but instead provides goodopacity on the web surface. A long dwell distance is used betweenapplication and doctoring, whereby a set immobilization layer has timeto form on the web surface whose dry matter content has risen. In thismanner, a greater amount of coating mix and better opacity are achieved.A blade doctor achieves excellent smoothness of the end product, but arod doctor may also be used.

The final calendering is carried out on a long-nip calender having atypical nip pressure of 1 to 12 MPa, a nip length of 30 to 280 mm and athermoroll temperature of 100 to 300°0 C. The belt hardness of along-nip calender is typically 80 to 100 ShA. The advantage provided bya long-nip calender lies in the excellent surface smoothness and glareachieved without reducing the stiffness and bulk of the product, as wellas a visually very even surface. When a long-nip calender is used, anyunevenness in the surface of the base web will not emerge during visualinspection due to the soft calendering belt and low nip pressure.

The method of the invention is especially suited for on-linearrangements but can also be used in off-line manufacturing systemswhere intermediate reeling is applied.

While there has been shown and described certain fundamental novelfeatures of the present invention as applied to a preferred embodimentthereof, it will be understood by those skilled in the art that variousomissions and substitutions and changes in the devices described herein,and in their operation, may be made by those skilled in the art withoutdeparting from the spirit and scope of the invention. It is expresslyintended that all combinations of those elements and/or method stepsthat perform substantially the same function and substantially the sameway to achieve the same results are within the scope of the invention.Substitutions of elements from one described embodiment to another arealso fully intended and contemplated. It is the intention, therefore, tobe limited only as indicated by the scope of the claims appended hereto.

1. A method for producing a calendered product, comprising the steps of: (a) forming a base web from a mixture of water and pulp supplied from a headbox and drying the base web by pressing and heating; (b) standardizing a cross-directional thickness of the base web across a width of the base web to form a standardized web, said standardizing comprising selectively steaming sections across the width of the base web during pressing; and (c) calendering the standardized web at least once using a long-nip calender for modifying at least one side of the standardized web.
 2. The method of claim 1, wherein said step (b) of standardizing comprises selectively diluting the mixture of water and pulp supplied from the headbox in sections across the width of the base web.
 3. The method of claim 1, wherein said step (b) of standardizing comprises selectively pressing sections of the base web across the width of the base web.
 4. The method of claim 1, wherein said step (b) of standardizing further comprises selectively heating sections of the base web across the width of the base web.
 5. The method of claim 1, wherein said step (b) of standardizing comprises selectively cooling sections of the base web across the width of the base web.
 6. The method of claim 1, wherein said step (b) of standardizing comprises wetting sections of the base web across the width of the base web.
 7. The method of claim 1, wherein said step (b) of standardizing further comprises selectively wetting sections of the base web with one of a film transfer coater and a spray coater across the width of the base web.
 8. The method of claim 1, wherein said step (b) of standardizing comprises treating the base web with a machine calender prior to said step (c).
 9. The method of claim 8, wherein said step of treating the base web with a machine calender comprises treating the base web with a zone-adjusted machine calender.
 10. The method of claim 1, wherein said step (c) of calendering the standardized web comprises coating the standardized web with at least one coating layer and calendering the coated web with the long-nip calender.
 11. The method of claim 10, wherein said step of calendering further comprises using a precalender having a nip length of less than 50 mm, a nip pressure that does not exceed 50 MPa, and a thermoroll temperature of 80 to 300° C., and wherein the long-nip calender has a nip length of 30 to 280 mm, a nip pressure of 1 to 12 MPa, a thermoroll temperature of 100 to 300° C., and a calender belt hardness of 80 to 100 ShA.
 12. The method of claim 8, wherein said step (c) of calendering the standardized web comprises coating the standardized web with at least one coating layer and calendering the coated web with the long-nip calender.
 13. method of claim 12, wherein said step of calendering further comprises using a precalender having a nip length of less than 50 mm, a nip pressure that does not exceed 50 MPa, and a thermoroll temperature of 80 to 300° C., and wherein the long-nip calender has a nip length of 30 to 280 mm, a nip pressure of 1 to 12 MPa, a thermoroll temperature of 100 to 300° C., and a calender belt hardness of 80 to 100 ShA.
 14. The method of claim 1, wherein said step (c) of calendering the standardized web comprises coating the standardized web with at least one coating layer and calendering the coated web with the long-nip calender.
 15. The method of claim 14, wherein said step of calendering further comprises using a precalender having a nip length of less than 50 mm, a nip pressure that does not exceed 50 MPa, and a thermoroll temperature of 80 to 300° C., and wherein the long-nip calender has a nip length of 30 to 280 mm, a nip pressure of 1 to 12 MPa, a thermoroll temperature of 100 to 300° C., and a calender belt hardness of 80 to 100 ShA.
 16. The method of claim 1, further comprising the step of measuring a thickness profile of the base web at at least one point of the length of the base web prior to said step (c) of calendering.
 17. The method of claim 16, wherein the thickness profile of the base web is measured with at least one actuator positioned upstream of the long-nip calender.
 18. The method of claim 1, wherein said steps are performed continuously on-line in a paper or board machine.
 19. The method of claim 1, further comprising the step of winding the standardized web onto a storage roll prior to said step (c) of calendering.
 20. The method of claim 1, wherein said step (b) of standardizing further comprises at least one of: (i) selectively diluting the mixture of water and pulp supplied from the headbox in sections across a width of the base web, (ii) selectively pressing sections of the base web across the width of the base web, (iii) selectively drying sections of the base web across the width of the base web, (iv) selectively cooling sections of the base web across the width of the base web, (v) selectively wetting sections of the base web across the width of the base web, (vi) treating the base web with a machine calender, and (vii) treating the base web with a zone-adjusted machine calender for selectively applying pressure to sections across the width of the base web.
 21. An apparatus for manufacturing a calendered paper or board comprising: a headbox effective for forming a base web from a mixture of water and pulp fed from said headbox; pressing means for removing water from the base web by pressing the base web; drying means for drying the base web by heating the base web; means for standardizing a cross-direction thickness of the base web across a width of the base web to form a standardized web, said standardizing means comprising means for selectively steaming sections across the width of the base web during pressing; and at least one calender comprising a long-nip calender for modifying at least one side of the standardized web.
 22. The apparatus of claim 21, wherein said headbox comprises a dilution adjusted headbox.
 23. The apparatus of claim 21, wherein said pressing means further comprises means for selectively steaming sections of the base web across the width of the base web.
 24. The apparatus of claim 21, wherein said means for standardizing the cross-direction thickness of the base web is capable of selectively and adjustably pressing sections of the base web across the width of the base web.
 25. The apparatus of claim 21, wherein said means for standardizing a cross-direction thickness of the base web comprises heating means for selectively heating sections of the base web across the width of the base web.
 26. The apparatus of claim 21, wherein said means for standardizing a cross-direction thickness of the base web comprises cooling means for selectively cooling sections of the base web across the width of the base web.
 27. The apparatus of claim 21, wherein said means for standardizing a cross-direction thickness of the base web comprises wetting means for selectively wetting sections of the base web across the width of the base web.
 28. The apparatus of claim 27, wherein said wetting means comprises one of a film transfer coater and a spray coater arranged upstream of said long-nip calender.
 29. The apparatus of claim 21, further comprising a machine calender for treating the base web upstream of a last of said at least one calendar.
 30. The apparatus of claim 29, wherein the machine calender comprises a zone-adjusted machine calender for selectively applying pressure to sections across the width of the base web.
 31. The apparatus of claim 21, further comprising a precalender and at least one coater for applying at least one coating layer onto the standardized web.
 32. The apparatus of claim 31, wherein said precalender has a nip length of less than 50 mm, a nip pressure that does not exceed 50 MPa, and a thermoroll temperature of 80 to 300° C., and said long-nip calender has a nip length of 30 to 280 mm, a nip pressure of 1 to 12 MPa, a thermoroll temperature of 100 to 300° C., and a calender belt hardness of 80 to 100 ShA.
 33. The apparatus of claim 29, further comprising a precalender and at least one coater for applying at least one coating layer onto the standardized web.
 34. The apparatus of claim 33, wherein said precalender has a nip length of less than 50 mm, a nip pressure that does not exceed 50 MPa, and a thermoroll temperature of 80 to 300° C., and said long-nip calender has a nip length of 30 to 280 mm, a nip pressure of 1 to 12 MPa, a thermoroll temperature of 100 to 300° C., and a calender belt hardness of 80 to 100 ShA.
 35. The apparatus of claim 21, further comprising a precalender and at least one coater for applying at least one coating layer onto the standardized web.
 36. The apparatus of claim 35, wherein said precalender has a nip length of less than 50 mm, a nip pressure that does not exceed 50 MPa, and a thermoroll temperature of 80 to 300° C., and said long-nip calender has a nip length of 30 to 280 mm, a nip pressure of 1 to 12 MPa, a thermoroll temperature of 100 to 300° C., and a calender belt hardness of 80 to 100 ShA.
 37. The apparatus of claim 21, further comprising means for measuring a thickness across the width of said base web at a point along the length of the base web upstream of the at least one calender.
 38. The apparatus of claim 37, wherein said means for standardizing the cross-directional thickness includes at least one actuator, and said means for measuring is effective for measuring the thickness across the width of the base web at a point upstream of a last one of the at least one actuator.
 39. The apparatus of claim 21, wherein said long-nip calender is an on-line calender in that the standardized web is received by said long-nip calender directly from the means for standardizing.
 40. The apparatus of claim 21, further comprising a reeler for reeling up the standardized web onto a storage reel before the web is fed to said at least one calender.
 41. The apparatus of claim 21, wherein said means for standardizing further comprises at least one of: (i) means for selectively diluting the mixture of water and pulp supplied from the headbox in sections across a width of the base web, (ii) means for selectively and adjustably pressing sections of the base web across the width of the base web, (iii) means for selectively drying sections of the base web across the width of the base web, (iv) means for selectively cooling sections of the base web across the width of the base web, (v) means for selectively wetting sections of the base web across the width of the base web, (vi) a machine calender, and (vii) a zone-adjusted machine calender for selectively applying pressure to sections across the width of the base web. 